Abstract

An investigation into the use of the Instron ElectroPuls E3000 for the purpose of fatigue crack growth rate testing of structural materials was conducted. The reference material used in this study was BIS812EMA steel and fatigue testing was performed in accordance with ASTM E 47-13. The ElectroPuls E3000 produced fatigue crack growth rate data (at a frequency of 10 Hz) that was consistent with previous testing performed on servohydraulic testing machines (at a frequency of 2 Hz). The apparatus was able to produce reliable data up to a frequency of approximately 40 Hz; the exact frequency limit depended on the R-ratio of the cyclic loading. An attempt was made to measure the threshold stress intensity factor range for BIS812EMA. The results indicate that for an Rratio of 0.5, the threshold stress intensity factor range is approximately 3.2 MPa·m½. Limitations of the test apparatus were identified under certain test conditions, for example, undershoot of the minimum load at high frequencies.

Executive Summary

An investigation into the applicability of the Electropuls E3000 test machine and associated apparatus for fatigue crack growth testing of structural materials was conducted. The Electropuls E3000 is an electrically actuated test machine that claims to be able to operate at frequencies "over 100 Hz" and has the potential to increase efficiency by decreasing test time, as compared with a servo-hydraulic test machine that, typically, has a maximum operating frequency of 10 Hz. The aims of the investigation were (i) to ensure that the ElectroPuls E3000 produced data consistent with previous testing, and (ii) to investigate any specific problems or technicalities of the test machine, associated apparatus, and software operation. Fatigue testing was performed in accordance with ASTM E 647-13 Standard Test Method for Measurement of Fatigue Crack Growth Rates. The reference material used in this study was BIS812EMA steel. This material was selected as its fatigue behaviour has been well characterised. The ElectroPuls E3000 produced fatigue crack growth rate data (at a frequency of 10 Hz) that was consistent with previous testing performed on servo-hydraulic testing machines (at a frequency of 2 Hz). Fatigue striation measurements obtained through quantitative fractography using a scanning electron microscope were consistent with results of other steels detailed in the literature. The ElectroPuls E3000, associated test apparatus, and software produced reliable data up to a frequency of approximately 40 Hz; the exact frequency limit depended on the R-ratio of the load cycle. Capitalising on the higher frequency capability of the apparatus and corresponding reduced test duration, an attempt was made to produce threshold stress intensity factor range data for BIS812EMA. This parameter had not been previously characterised for this material. For an R-ratio of 0.5, the threshold stress intensity factor range was approximately 3.2 MPa·m½. However, it is recommended that this threshold test be repeated to confirm this result. Through the course of investigating the behaviour of the test apparatus, limitations were identified under certain conditions, for example, undershoot of the minimum load was observed at high frequencies. Consequently, it is recommended that the high frequency load cell is used to verify small loads at high frequencies. It has been demonstrated that the ElectroPuls E3000 can, with due care, be successfully used to obtain crack growth rate data on structural materials at frequencies greater than those achievable on servo-hydraulic test machines.